This invention relates to personal computers, and more particularly to the provision of shielding for attenuating the emission of electromagnetic radiation and the like from an enclosure for such computers.
Personal computer systems in general and IBM personal computers in particular have attained widespread use for providing computer power to many segments of today's modern society. Personal computer systems can usually be defined as a desk top, floor standing, or portable microcomputer that consists of a system unit having a single system processor and associated volatile and non-volatile memory, a display monitor, a keyboard, one or more diskette drives, a fixed disk storage, and an optional printer. One of the distinguishing characteristics of these systems is the use of a motherboard or system planar to electrically connect these components together. These systems are designed primarily to give independent computing power to a single user and are inexpensively priced for purchase by individuals or small businesses. Examples of such personal computer systems are IBM's PERSONAL COMPUTER AT and IBM's PERSONAL SYSTEM/2 Models 25, 30, 50, 60, 70 and 80.
These systems can be classified into two general families. The first family, usually referred to as Family I Models, use a bus architecture exemplified by the IBM PERSONAL COMPUTER AT and other "IBM compatible" machines. The second family, referred to as Family II Models, use IBM's MICRO CHANNEL bus architecture exemplified by IBM's PERSONAL SYSTEM/2 Models 50 through 80. The Family I models typically have used the popular INTEL 8088 or 8086 microprocessor as the system processor. These processors have the ability to address one megabyte of memory. The Family II models typically use the high speed INTEL 80286, 80386, and 80486 microprocessors which can operate in a real mode to emulate the slower speed INTEL 8086 microprocessor or a protected mode which extends the addressing range from 1 megabyte to 4 Gigabytes for some models. In essence, the real mode feature of the 80286, 80386, and 80486 processors provide hardware compatibility with software written for the 8086 and 8088 microprocessors.
It is well known that the components of a personal computer housed within an enclosure and supported from the chassis or connected with the planar board are capable of emitting electromagnetic radiation at various frequencies and that standards have been established for limiting the emission of such energy to various limits depending on the environment of use of the computer. Further, it is known that higher speed processors and circuits associated with such processors, such as those specifically mentioned above, typically emit radiation of differing frequencies and amounts than the earlier designed, slower processors. Heretofore, shielding has been accomplished in various ways, including providing metal enclosures and/or coating or lining the enclosures and covers provided. In achieving shielding in these ways, and attenuating radiation, it has been noted that openings provided in such enclosures and covers can present particularly difficult problems in shielding.
It has also become desirable to provide for the possibility that a personal computer may be provided with direct access storage devices such as magnetic disk, optical disk, tape backup, and other drives. In making provision for such additions, the chassis and enclosure for a personal computer may be provided with areas, known as "bays", designed to receive and accommodate additional devices. While such bays provide flexibility in arranging the components of a personal computer, they also present additional openings to be dealt with in arranging shielding.
As the development of personal computer technology has advanced, personal computers have been enabled to incorporate 10 increasingly higher data handling speeds in processors, data storage devices, and memory. Such higher speeds bring with them greater emission of electromagnetic radiation, increasing the demands placed on enclosures for the attenuation of such emissions. Other terms used to refer to such requirements have been electromagnetic compatibility and the suppression of electromagnetic interference. In efforts to bring emissions within the required standards while attaining the sought for high speeds, designs have moved toward a completely grounded enclosure with minimal gaps and openings.